Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $154.54   7.144%   $165.5803   $165.58   $165.60   $165.60  
  Purchase #2 $180.58   4.416%   $188.5544   $188.55   $188.55   $188.60  
  Purchase #3 $50.41   11.355%   $56.1341   $56.13   $56.15   $56.10  
  Purchase #4 $203.59   12.855%   $229.7615   $229.76   $229.75   $229.80  
  Purchase #5 $60.64   9.697%   $66.5203   $66.52   $66.50   $66.50  
  Purchase #6 $200.34   11.596%   $223.5714   $223.57   $223.55   $223.60  
  Purchase #7 $77.62   8.233%   $84.0105   $84.01   $84.00   $84.00  
  7 purchase totals = $927.72       $1,014.1325   $1,014.12   $1,014.10   $1,014.20